Alkylnaphthalene compounds are important heating media and solvents for pressure sensitive paper, and thus are used extensively. Alkylnaphthalene compounds are also widely used in the manufacture of naphthalenedicarboxylic acid, and have recently received attention as raw materials for polyester, and naphthol compounds.
There are various alkylnaphthalene compounds (e.g., depending upon the position of the alkyl group substituent). However, 2-position-monosubstituted alkylnaphthalene compounds and 2,6-position-disubstituted alkylnaphthalene compounds are particularly useful.
Methods of preparing alkylnaphthalene compounds which have been generally adopted in the conventional art consist of reacting a compound of naphthalene or a monoalkylnaphthalene with an olefin in the presence of a catalyst composed of a Lewis acid such as AlCl.sub.3, BF.sub.3, etc., such as disclosed in Japanese Publication for Unexamined Patent Application No. 230645/1988, No. 61435/1989 and No. 197447/1989 (Tokukaisho No. 63-230645 and No. 64-61435, Tokukaihei No. 1-197447). However, these methods suffer from various drawbacks. For instance, the recovery and re-utilization of the catalyst employed is difficult and the strong corrosiveness of the catalyst restricts the materials use with industrial equipment. Also, among the different alkylnaphthalene compounds, 2-position-monosubstituted alkylnaphthalene compounds and 2,6-position-disubstituted alkylnaphthalene compounds are particularly valuable, as stated earlier. However, with the above described methods, isomerization is likely to take place during the chemical reaction, thereby giving rise to a large amount of 1-position-monosubstituted alkylnaphthalene compounds.
Some methods employ a silica-alumina catalyst or a zeolite catalyst instead of Lewis acid, such as disclosed kn Japanese Publication for Unexamined Patent Application No. 215647/1988, No. 9942/1989 and No. 135731/1989 (Tokukaisho No. 63-215647, No. 64-9942 and Tokukaihei No. 1-135731). However, these methods present industrial problems. For example, conversion, that denotes the proportion of raw material consumed, as well as the yield of the desired chemical compounds, are low whereby a large amount of catalyst is needed. In addition, isomerization is likely to take place.